Process for ultra-thin body SOI devices that incorporate EPI silicon tips and article made thereby

ABSTRACT

The invention relates to a transistor that includes an ultra-thin body epitaxial layer that forms an embedded junction with a channel that has a length dictated by an undercut under the gate stack for the transistor. The invention also relates to a process of forming the transistor and to a system that incorporates the transistor.

FIELD OF THE INVENTION

An embodiment of the present invention relates generally to integratedcircuit fabrication. More particularly, an embodiment of the presentinvention relates to a method of fabricating an ultra-thin body siliconon oxide (SOI) device.

BACKGROUND OF THE INVENTION DESCRIPTION OF RELATED ART

Transistor technology has progressed to include large-scale integration(LSI), very large-scale integration (VLSI), and ultra large-scaleintegration (ULSI), with further improvements appearing on the technicalhorizon. One challenge for ULSI is that more transistors must beincorporated into an integrated circuit (IC), while attempting todecrease the overall size of the semiconductive substrate. Onerequirement is that the semiconductive channel length is preferablyshortened in order to further assist the miniaturization process. Onechallenge is that photolithographic techniques cause a criticaldimension to be the smallest feature patternable. For example, the widthof a gate stack may be such a critical dimension. Other challengesinclude proper electrical isolation between adjacent devices in the faceof the relentless pressure to crowd devices closer to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the manner in which embodiments of the presentinvention are obtained, a more particular description of the inventionbriefly described above will be rendered by reference to specificembodiments thereof which are illustrated in the appended drawings.Understanding that these drawings depict only typical embodiments of theinvention that are not necessarily drawn to scale and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an elevational cross-section of a semiconductor structure thatreveals a gate stack precursor according to an embodiment of theinvention;

FIG. 2 is an elevational cross-section of the semiconductor structuredepicted in FIG. 1 after further processing;

FIG. 3 is an elevational cross-section of the semiconductor structuredepicted in FIG. 2 after further processing;

FIG. 4 is an elevational cross-section of the semiconductor structuredepicted in FIG. 3 after further processing;

FIG. 5 is an elevational cross-section of the semiconductor structuredepicted in FIG. 4 after further processing;

FIG. 6 is an elevational cross-section of the semiconductor structuredepicted in FIG. 5 after further processing;

FIG. 7 is an elevational cross-section of the semiconductor structuredepicted in FIG. 6 after further processing;

FIG. 8 is an elevational cross-section of the semiconductor structuredepicted in FIG. 7 after further processing;

FIG. 9 is an elevational cross-section of the semiconductor structuredepicted in FIG. 8 after further processing;

FIG. 10 is an elevational cross-section of the semiconductor structuredepicted in FIG. 9 after further processing;

FIG. 11 is an elevational cross-section of the semiconductor structuredepicted in FIG. 10 after further processing;

FIG. 12 is an elevational cross-section of the semiconductor structuredepicted in FIG. 11 after further processing;

FIG. 13 is an elevational cross-section of the semiconductor structuredepicted in FIG. 12 after further processing;

FIG. 14 is an elevational cross-section of the semiconductor structuredepicted in FIG. 13 after further processing;

FIG. 15 is a chart that describes a process flow embodiment;

FIG. 16 is a top plan schematic view of a silicon wafer that contains anultra-thin body SOI device embodiment;

FIG. 17 is a schematic view of a circuit module according to anembodiment;

FIG. 18 is a schematic view of an electronic system; and

FIG. 19 shows a further embodiment of an electronic system as a computersystem.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates a process flow that forms an ultra-thinbody silicon-on-insulator (SOI) transistor. FIG. 1 is an elevationalcross section that illustrates a semiconductor device 10 duringfabrication. Semiconductor device 10 includes a substrate 12 that by wayof non-limiting example, is a p-type metal oxide semiconductor device(PMOS) or an n-type metal oxide semiconductor device (NMOS). Accordingto the present invention, one embodiment of substrate 12 includes an SOIconfiguration. Accordingly, substrate 12 has an SOI insulator layer 14,and an SOI silicon layer 16. The formation of the SOI configuration iscarried out according to known technique. Although an SOI configurationis depicted, other isolation structures may be added such as localisolation of silicon (LOCOS), recessed LOCOS, or shallow trenchisolation (STI).

A gate dielectric layer 18 is formed on the upper surface 20 ofsubstrate 12 as shown in FIG. 1. In one embodiment, gate dielectriclayer 18 is a nitride oxide layer that is formed to a thickness in arange from about 5 Å to about 30 Å. In one embodiment, gate dielectriclayer 18 is a nitrided oxide layer that has a thickness of about 8 Å. Inother embodiments, gate dielectric layers such as oxides, nitrides,high-k materials, and combinations thereof are formed. A gate electrode22 is formed on gate dielectric layer 18. In one embodiment, gateelectrode 22 is formed in a thickness range from about 1,000 Å to about3,500 Å that is blanket deposited, doped polysilicon. Doping may be insitu or it may follow patterning of the blanket depositing that resultsin gate electrode 22 with photolithographic techniques known in the art.It is to be appreciated that other well known patterning techniques maybe utilized to pattern the blanket-deposited polysilicon layer into gateelectrode 22 including submicron lithography techniques, such as e-beamand x-ray, and subphotolithographic patterning techniques known in theart. According to one process flow of the present invention gateelectrode 22 has a width, W, in a lower range from about 100 nanometers(nm) to about 50 nm. Additionally, although gate electrode 22 isrepresented as a polysilicon electrode, other embodiments of gateelectrode 22 can be but is not limited to a metal gate, a singlecrystalline silicon gate, or combinations thereof.

FIG. 2 illustrates further processing. A spacer first layer 24 is formedover substrate 12 including oxide gate dielectric layer 18 and the topand sides of gate electrode 22. In one embodiment, a spacer first layer24 is formed to a thickness in a range from about 50 Å to about 300 Å.Spacer first layer 24 is preferably formed thick enough to electricallyisolate a subsequently deposited semiconductive film from gate electrode22. In one embodiment, spacer first layer 24 is an oxide film that isformed by what is commonly referred to as a hotwall process to achieve ahermetic seal of gate electrode 22 and the edges of gate dielectric 18.By forming an oxide spacer first layer 24 directly on gate electrode 22a hermetic seal is formed and hot electron lifetime of the fabricatedtransistors is extended.

In one embodiment, spacer first layer 24 is spacer etched to formsidewall spacers for the MOS device. As depicted in FIG. 3, the spacerlayer has been anisotropically dry etched to form a sidewall firstspacer 26 which runs along laterally opposite sidewalls of gateelectrode 22.

After the formation of an oxide sidewall first spacer 26, a nitridesidewall second spacer 28 is formed under a similar process flow. Anitride layer is blanket deposited over gate electrode 22 and sidewallfirst spacer 26 as depicted in FIG. 4. Thereafter, an anisotropic spaceretch follows. According to an embodiment, a silicon nitride layer isblanket deposited by a low pressure chemical vapor deposition (LPCVD)process by reacting ammonia (NH₃) and dichlorosilane (DCS) at a pressurein a range from about 25 milliTorr (mTorr) to about 100 mTorr, and at atemperature in a range from about 60° C. to about 100° C. In onespecific embodiment, the NH₃ and DCS are deposited at about 75 mTorr andabout 80° C.

Although a silicon nitride layer is hot-wall deposited in oneembodiment, because of the hermetic seal that forms, any other suitableinsulating layer, such as a deposited oxide or a composite oxide/siliconnitride film, can be used if a specific application is selected.According to an embodiment, nitride second spacer 28 is formed byanisotropically plasma etching the silicon nitride spacer layer usingchemistry including C₂ F₆ and a power in a range from about 100 watts toabout 300 watts. In one embodiment, a power of about 200 watts isapplied. The anisotropic etch is continued until all of the material hasbeen removed from the upper surface 20 and from the top of gateelectrode 22. The final thickness of first spacer 26 and second spacer28 may each be in a range from about 50 Å to about 300 Å. In oneembodiment, the thickness of first spacer 26 is in a range from about 50Å to about 300 Å; second spacer 28 is at least as thick or thicker.

In an alternative embodiment, both the oxide first spacer layer and thenitride second spacer layer are deposited, and a composite spacer etchrecipe is carried out that forms second spacer 28, followed by firstspacer 26. In this process flow, the spacer etch that forms secondspacer 28 need not have selectivity to the silicon of gate electrode 22or to SOI silicon 16. However, selectivity to the spacer first layer ispreferred if selectivity to silicon is not present. Accordingly, asingle deposition tool may be utilized to form spacer first- and secondlayers in situ, and a single etch tool may be utilized to form secondspacer 28, followed by first spacer 26, likewise in situ.

After the spacer etch(es) the structure can be cleaned by an HF cleanaccording to conventional technique. In one embodiment, the HF clean iscarried out for about 2 minutes. In one embodiment, the HF clean isfollowed by a hydrogen bake at a temperature of about 900° C. for about2 minutes. The hydrogen bake can remove surface oxidation.

Although first spacer 26 is represented as an oxide and second spacer 28is represented as a nitride, it is understood that other combinationembodiments are contemplated. For example, combinations include an oxidefirst spacer and a nitride second spacer, a nitride first spacer and anoxide second spacer, an oxide first spacer and an oxide second spacer,and a nitride first spacer and a nitride second spacer. In eachembodiment, an etch selectivity differentiation is an alternativecharacteristic, where the first spacer layer and the second spacer layermay be retained in other regions of the substrate as protection untilprocessing in these regions is undertaken.

FIG. 5 illustrates further processing. After the formation of firstspacer 26 and second spacer 28, an elevated silicon first layer 30 isformed upon upper surface 20 of substrate 12. The same process flow alsoforms an elevated polysilicon first layer 32 and above and on the gateelectrode 22. Upper surface 20 includes SOI silicon 16 that acts as acrystal lattice seed layer to enable epitaxial monocrystalline growththat follows the crystal lattice of SOI silicon 16. In one embodiment,SOI silicon 16 is in a range from about 50 Å to about 400 Å. In oneembodiment, silicon first layer 30 and polysilicon first layer 32 aresubstantially undoped, as they are often entirely removed according toselected embodiments. However, doping thereof may be done where thedoping will assist process integration. In the formation of siliconfirst layer 30 and polysilicon first layer 32, a silicon or siliconalloy film is selectively deposited onto upper surface 20 and onto theexposed silicon of gate electrode 22. Selective deposition of siliconforms silicon only on silicon containing surfaces. The deposited siliconcan be a silicon film of substantially only silicon or it can be asilicon alloy such a silicon germanium. A silicon film can beselectively deposited by heating to a temperature of 600-900° C. andproviding a deposition gas such as dichlorosilane silane (SiH₂Cl₂) andHydrogen (H₂). A silicon germanium alloy (Si_(1-x)Ge_(x)) can beselectively deposited by heating to a temperature between 700-750° C.and providing a deposition gas such as dichlorosilane at a rate ofbetween 10-300 sccm, 1% hydrogen diluted germane (GeH₄) at a rate ofbetween 10-200 sccm, and H₂ at a rate of about 20 slm into a CVD chamberthat is maintained at a pressure between 10-760 torr. A dopant gas suchas diborane, phosphine, and arsine can be included in the process gasmix if a doped silicon or silicon alloy film is desired.

FIG. 6 illustrates further processing and second spacer 28 has beenstripped such as by a wet etch that is selective to first spacer 26 andto exposed silicon. Thereafter, a semi-iosotropic dry etch is carriedout to form a self-aligned recess 34 as depicted in FIG. 7. Self-alignedrecess 34 forms in what remains of the SOI silicon 16, aligned alonglaterally opposite sidewalls of gate electrode 18. In one embodiment, asemi-isotropic etch process flow is used to form self-aligned recess 34.An isotropic etch not only etches vertically into the SOI silicon layer16 (FIG. 6), but it also etches horizontally beneath first spacer 26 andgate electrode 22. The semi-isotropic etch of the SOI silicon forms agate-masked residue 36 of the SOI silicon 16 and a lateral residue 38thereof. The etch also forms an undercut 40. Accordingly the transistorchannel length, which is measured by gate-masked residue 36 of SOIsilicon 16, may be shorter than width, W.

In one embodiment, undercut etching is produced by using asemi-isotropic dry etch process in a parallel plate radio frequency (RF)plasma etching system. A wet etch may also be used to form self-alignedrecess 34 and undercut 40. In the semi-isotropic dry etch, the chemistryincludes a gas mix chemistry of sulfur hexafluoride (SF₆) and helium(He) and process conditions which favor isotropy. Such conditionsinclude a low enough pressure to allow the mean-free path of an etchantgas to start approaching anisotropy, but to retain basically isotropicperformance that will also achieve the undercut 40 beneath gateelectrode 22 and gate dielectric layer 18. Additionally a low RF powerdensity is selected. In one embodiment of the present invention, aprocess pressure of about 900 mTorr, a gap of about 1.1 cm, an RF powerof about 100 W, a He flow of about 150 sccm, and an SF₆ flow of about100 sccm is used. In this embodiment, the RF power is varied in a rangefrom about 50 W to about 200 W, and the process pressure is varied atranges above about 500 mTorr.

According to the present invention, the semi-isotropic dry etch processflow produces undercut 40 and the etch chemistry is also selective tothe gate dielectric layer 18, the SOI insulator layer 14, and the firstspacer 26. In this way first spacer 26 and gate dielectric layer 18 arenot significantly etched during the silicon etch. In one embodiment ofthe etch process flow that is used to form the undercut 40, the etchchemistry is slightly oxidizing such that the etch conditions cause alateral portion 42 of the gate dielectric layer 18 or first spacer 26that is exposed during the recess etch to thicken. Thereby, the gateedge leakage at the tip overlap region of the gate stack is reduced. Athicker gate dielectric layer at the gate edge also increases thebreakdown voltage of the gate.

Because an over-etch would undercut the gate electrode 22 in SOI siliconlayer 16 and continue to reduce gate-masked residue 36 until it would bedestroyed, the lateral recess etch process flow of the present inventionacts to control the lateral etch rate to between about 1 Å/second toabout 30 Å/second. In one embodiment, the controlled lateral etch ratecauses an inflection point 44 to form in what is left of the SOI siliconlayer 16 as depicted in FIG. 7. According to the present invention, thetransistor channel length is definable approximately from the inflectionpoint 44 to the opposite inflection point 44. Hence, where the minimumfeature is a gate width, W (FIG. 1), a channel length is less than widthW. With this geometry, a large L_(MET) (metallurgical channel length orphysical channel length) is achieved during the off state of thetransistor (low I_(off)) while a smaller L_(MET) is achieved during theon state when the channel is formed. A smaller L_(MET) during the onstate causes a smaller channel resistance and enhances a higher I_(on).In one embodiment, the gate dielectric has a width, W, and the L_(MET)has a length that is in a range from about 0.2 W to about 0.99 W. Inanother embodiment, the gate dielectric has a width, W, and the L_(MET)has a length that is in a range from about 0.3 W to about 0.8 W. Inanother embodiment, the gate dielectric has a width, W, and the L_(MET)has a length that is in a range from about 0.4 W to about 0.7 W.

Where the minimum feature, such as W by way of non-limiting example, isbased upon a commonly referred-to metric, such as a 0.25 micrometer(micron) process, it is understood that the actual measurement may varyfrom 0.25 actual microns. By way of further reference, according todesign rules, a minimum feature may be part of the metric of device 10depicted in the figures. For example, photolithography process flows mayhave minimum features that are 0.25 microns, 0.18 microns, and 0.13microns. It is understood that the various metrics such as 0.25 micronsmay have distinctly different dimensions in one business entity from acomparative business entity. Accordingly, such metrics, althoughquantitatively called out, may differ between a given two businessentities. Other minimum features that may be accomplished in the futureare applicable to the present invention.

In an embodiment of the present invention self-aligned recess 34 has amaximum vertical depth the stops on the SOI insulator layer 14 due toetch selectivity. In this embodiment, self-aligned recess 34 is betweenabout 100 Å and about 1,500 Å below the former location of upper surface20 and extends between about 25 Å to about 200 Å horizontally orlaterally beneath the edge 46 of the gate stack 48. The deepestpenetration into the SOI silicon layer 16 occurs at the inflection point44 if present. It is to be appreciated that alternative processconditions and etch chemistries may be elected to generate other recessgeometry profiles of undercut 40. The semi-isotropic dry etchsubstantially removes the epitaxial first film 30 (FIG. 6) and thepolysilicon first film 32 (FIG. 6) and begins to etch into the SOIsilicon layer 16 and the polysilicon of gate electrode 22.

After the etch, it is noted that there is exposed a self-aligned portion50 of SOI insulator layer 14 as depicted in FIG. 8. According to anembodiment, an ultra-thin body epitaxial second layer 52 and apolysilicon second layer 54 are formed. Epitaxial second layer 52includes a raised epitaxial tip 56 that may or may not be at a levelthat is higher than the original placement of the upper surface 20 ofthe original SOI silicon 16. Further, raised epitaxial tip 56 mayapproach the same height as gate stack 48 according to givenapplications. In one embodiment, raised epitaxial tip 56 is up to about10% as high as gate stack 48, when measured from upper surface 20. Inone embodiment, raised epitaxial tip 56 is up to about 50% as high asgate stack 48, when measured from upper surface 20. In one embodiment,raised epitaxial tip 56 is up to about 90% as high as gate stack 48,when measured from upper surface 20. The height of gate stack 48, forthese purposes includes any conductive material of the finished device.

Epitaxial second layer 52 also includes an embedded source/drainjunction 58 with gate-masked residue 36. Epitaxial second layer 52 takesas it seed sources, gate-masked residue 36 of SOI silicon layer 16 andlateral residue 38 thereof.

Process conditions cause the epitaxial second layer 52 to form a closureseam 60 somewhere between the gate-masked residue 36 of SOI siliconlayer 16 and lateral residue 38 thereof. Closure seam 60 is depicted inan arbitrary location and at an arbitrary angle and shape, but it is tobe understood that in one embodiment, it has the appearance of adislocation in an otherwise substantially epitaxial and monocrystallinelayer 52. Closure seam 60 may be formed at an angle that minimizesincreased resistivity as electrical current flows from raised tip 56 andthrough embedded junction 58.

Again, it is noted that above gate electrode 22, an ultra-thin bodypolysilicon second layer 54 simultaneously forms during the formation ofepitaxial second layer 52. In one embodiment, a film of boron-dopedsilicon is formed using SiH₂Cl₂ based chemistry such that the depositionis highly selective to the spacer 26, such that the boron-doped silicondoes not form on, or adhere to the spacer 26. However, the recesses aresubstantially filled by this deposition process. The recess can becompletely filled by this process.

In an alternative embodiment, boron-doped SiGe can be used in place ofboron-doped silicon to form the film that fills the recess. Typically,epitaxial material is deposited such that its top surface is above theplane of the original surface of the substrate.

In one embodiment, a boron-doped silicon film is formed by a selectivedeposition. A selective deposition of silicon, or a silicon alloy suchas silicon germanium, forms silicon, or the silicon alloy, or theexposed silicon surfaces. For example, a selective deposition ofboron-doped silicon creates the ultra-thin body second layers 52, 54.Such a film can be selective deposited by heating the substrate to atemperature from about 600° to about 900° C. and metering a depositiongas such as dichlorosilane and hydrogen. Similarly, a silicon germaniumalloy can be selectively deposited by heating to a temperature betweenabout 700° C. and about 750° C., providing a deposition gas mix ofdichlorosilane at a rate from about 10 sccm to about 300 sccm, 1%hydrogen-diluted germane gas at a rate from about 10 sccm to about 25sccm, and hydrogen from about 15 slm to about 25 slm into a CVD chamberthat is maintained at a pressure from about 50 torr to about 760 torr,or ambient pressure. A dopant gas such as diborane, phosphine, orarsine, can be included in the process gas mixture if a doped silicon orsilicon alloy film is to be formed.

A highly doped (>5×10²⁰ atoms/cm²) n-type silicon germanium epitaxialfilm can be selectively deposited onto silicon surfaces by thermalchemical vapor deposition utilizing a deposition gas mix includinggermane, dichlorosilane, arsine, and hydrogen while maintaining thesubstrate at a temperature between about 700° C. and about 750° C. andmaintaining a relatively high deposition pressure of greater than about50 torr but less than atmospheric during film deposition. Such a processwill form a substantially uniformly doped n-type silicon germaniumepitaxial film.

Similarly, a p-type silicon germanium alloy can be formed bydecomposition of approximately 20 sccm of dichlorosilane, approximately130 to 180 sccm of 1% hydrogen-diluted germanium, and a p-type dopantsource, such as approximately 5-50 sccm of 1% hydrogen-diluted diborane(B₂H₆) at a temperature between approximately 600° C. and 800° C. In oneembodiment, a temperature of about 700° C. and a relatively highpressure of about 50 torr is used. In order to decrease the selectivityof the decomposition process, approximately 25 to 50 sccm of HCl can beadded to the gas deposition mixture.

Those skilled in the art and having the benefit of this disclosure, willrecognize that, the deposition process is such that selectivity to oxidein field oxide regions, or shallow trench isolation regions is alsoachieved.

Further processing is carried out to protect the achieved structures andto prepare them for metallization connection. Raised episilicon tip 56is further processed to increase the conductivity of the device. Asdepicted in FIG. 9, a first dielectric layer 62 is formed over substrate12 by CVD. First dielectric layer 62 may be selected from an oxide, anitride, an oxynitride, and the like. In one embodiment, firstdielectric layer 62 has thickness in a range from about 50 Å to about100 Å. Thereafter a second dielectric layer 64 is formed over substrate12 by CVD. Second dielectric layer 64 may be selected from an oxide, anitride, an oxynitride, and the like, so long as it has at least one ofa significant oxidation- or etch response difference from firstdielectric layer 62. In one embodiment, second dielectric layer 64 has athickness in a range from about 500 Å to about 1,800 Å. The formation ofboth first and second dielectric layers 62, 64 are preferably carriedout at temperatures that conserve the thermal budget.

After the formation of first- and second dielectric layers 62 and 64,respectively, a spacer etch is carried out to form a composite spacer 66adjacent to sidewall first spacer 26 as depicted in FIG. 10. Becausefirst- and second dielectric layers 62 and 64, respectively, may be afirst oxide and a second nitride material, silicon nitride and oxideetch process may be used. In another embodiment, the functionalequivalent of composite spacer 66 may be formed from a single nitride oroxide dielectric. In one embodiment, composite spacer 66 is used toseparate a silicide on the source/drain regions from a silicide on thegate region. In one embodiment, composite spacer 66 is used to offset ahigh energy high dose implant from the active channel region. In anembodiment of the present invention composite spacer 66 has a thicknessin a range from about 500 Å to about 2,000 Å.

In one process flow embodiment, depicted in FIG. 11, a source/drainimplant is made. The source/drain implant 68 is made in the raisedepitaxial tip 56 in alignment with the outside edges of composite spacer66 in order to increase the doping concentration of the source/draincontact regions and the polysilicon layer 54. Spacers 26 and 66 and gateelectrode 22 prevent doping of the channel region (the gate-maskedresidue 36) beneath the gate as well as the ultra-thin body epitaxialfilm disposed beneath the spacers. Accordingly, the source/drain implantdoes not affect the ultra-thin body epitaxial SOI film at the embeddedsource/drain junction 58.

After the optional source/drain implant, a salicidation process iscarried out to form a low resistance film for the gate stack 48 abovegate electrode 22 and for the elevated raised epitaxial tip 56. In oneembodiment, a refractory metal film 70 is blanket deposited oversubstrate 12 as depicted in FIG. 12. The refractory metal may beselected from nickel (Ni), cobalt (Co), palladium (Pd) and the like. Therefractory metal may also be selected from aluminum (Al), titanium (Ti),tungsten (W), ti-tungsten (TiW), chromium (Cr), and the like. Otherrefractory metals may be selected according to integration with a givenprocess flow and/or a given end product. The refractory metal film 70 isblanket deposited. In an embodiment of the present invention a cobaltfilm is deposited to a thickness in a range from about 100 Å to about200 Å. Refractory metal film 70 may be formed by any well known methodincluding sputter deposition such as physical vapor deposition (PVD) orby CVD. An Endura® system, made by Applied Materials (AMAT) of SantaClara, Calif. can be used to sputter deposit refractory metal film 70.

After the formation of refractory metal film 70, a protective layer 72,of for example titanium nitride, is deposited directly onto refractorymetal film 70. In one embodiment, protective layer 72 is titaniumnitride that is deposited to a thickness in a range from about 500 Å toabout 200 Å. Protective layer 72 can be formed by any well knowntechnique such as by PVD with an Applied Materials Endura system or itcan be formed by CVD. Protective layer 72 protects the underlyingrefractory metal layer 70 from oxidation during a subsequent silicideanneal.

After the formation of protective layer 72, substrate 12 is heated to atemperature and for a period of time sufficient to cause refractorymetal film 70 to react with underlying silicon to form a refractorymetal silicide film as depicted in FIG. 13. The heating process may becarried out in an inert atmosphere such as argon (Ar) or in someinstances, nitrogen (N₂) and a temperature in a range from about 400° C.to about 500° C. for a time range from about 45 seconds to about 2minutes. In one embodiment, heating is carried out at about 450° C. forabout 90 seconds. Substrate 12 can be suitably annealed in an AMAT 5000®or AMAT 5200® RTP tool. Such a heating process causes the reaction ofthe refractory metal film 70 and underlying silicon for form a lowsheet-resistance phase film 74 that has a mean sheet resistance of about11 Ohms per square.

FIG. 14 depicts further processing. Any unsalicided refractory metalfilm 70 is removed, for example, with a 50:1 buffered HF wet etch for atime period from about 90 seconds to about 150 seconds. After the wetetch, the low sheet-resistance phase film 74 remains on the source/drainregions and on gate stack 48 are electrically isolated from one anotherby the spacers 26 and 66.

The present invention has been depicted with respect to a p-MOS devicehaving a specific structure. However, it is to be appreciated that thepresent invention can be used to form an embedded epitaxial junction inan undercut with raised a epitaxial silicon tip and a low resistancerefractory metal silicide on an arsenic or phosphorus (n-type) dopedfilm. For example, the process of the present invention can be used toform a low resistance silicide on an n-MOS device formed by the abovedescribed process except that the recesses are formed in a p-typesubstrate region having a conductivity in the range of about 1×10¹⁷/cm³to about 1×10¹⁹/cm³ and are filled with the an n-type silicon filmhaving a doping density between about 1×10¹⁸/cm³ to about 3×10²¹/cm³. Inone embodiment the concentration is about 1×10²⁰/cm³. For example, ann-type silicon film can be formed by decomposition of dichlorosilaneSiH₂Cl₂ at a flow rate from about 20 sccm to about 250 sccm and ann-type dopant source of hydrogen-dilutes phosphane PH₃ at a flow ratefrom about 100 sccm to about 400 sccm and at a temperature in a rangefrom about 500° C. to about 700° C. In one embodiment, about 200 sccmdichlorosilane and about 200 sccm phosphane is metered to substrate 12at about 575° C. As set forth herein, where selectivity is preferred,hydrogen chloride may be metered to substrate at a flow rate from about5 sccm to about 60 sccm.

FIG. 15 is a process flow diagram that illustrates a process embodiment.The process begins with providing 150 a gate stack upon asilicon-on-insulator (SOI) substrate. Thereafter, a first spacer and asecond spacer are formed 152 on the gate stack. An elevated epitaxialfirst layer is grown 154 upon the substrate, and the second spacer isremoved 156. Thereafter at the gate stack, a gate stack undercut isetched, and a source/drain epitaxial second film is formed 158 at thegate stack undercut.

One embodiment of the inventive ultra-thin body SOI device includes anelectronic system. With reference to FIG. 16, a semiconductor die 160may be produced from a semiconductor wafer 162 that contains the MOSdevice 10. A die 160 is an individual pattern, typically rectangular, onsubstrate 12 that contains circuitry to perform a specific function. Asemiconductor wafer 162 will typically contain a repeated pattern ofsuch dies 160 containing the same functionality. Die 160 may furthercontain additional circuitry to extend to such complex devices as amonolithic processor with multiple functionality. Die 160 is typicallypackaged in a protective casing (not shown) with leads extendingtherefrom such as bump pad layers that provide access to the circuitryof the die 160 for unilateral or bilateral communication and control. Inone embodiment, die 160 is encased in a chip package (not shown) such asa chip-scale package (CSP).

As shown in FIG. 17 two or more dies 160, one of which including atleast one ultra-thin body SOI device as is depicted in FIGS. 1-14 inaccordance with the present invention may be combined, with or withoutprotective casing, into a circuit module 170 or chipset to enhance orextend the functionality of an individual die 160. Circuit module 170may be a combination of dies 160 representing a variety of functions, ora combination of dies 160 containing the same functionality. Someexamples of a circuit module 170 include memory modules, device drivers,power modules, communication modems, processor modules andapplication-specific integrated circuit (ASIC) modules, and may includemulti-layer, multi-chip modules. Circuit module 170 may be asub-component of a variety of electronic systems, such as a clock, atelevision, a cell phone, a personal computer, an automobile, anindustrial control system, an aircraft and others. Circuit module 170has a variety of leads 172 extending therefrom providing unilateral orbilateral communication and control.

FIG. 18 shows an electronic system 180 containing one or more circuitmodules 170 as described above containing at least one instance of theinventive ultra-thin body SOI device 10 as described herein. Electronicsystem 180 generally contains a user interface 182. User interface 182provides a user of the electronic system 180 with control or observationof the results of the electronic system 180. Some examples of userinterface 182 include the keyboard, pointing device, monitor and printerof a personal computer; the tuning dial, display and speakers of aradio; the ignition switch and gas pedal of an automobile; and the cardreader, keypad, display and currency dispenser of an automated tellermachine. User interface 182 may further describe access ports providedto electronic system 180. Access ports are used to connect an electronicsystem to the more tangible user interface components previouslyexemplified. One or more of the circuit modules 170 may include aprocessor providing some form of manipulation, control or direction ofinputs from or outputs to user interface 182, or of other informationeither preprogrammed into, or otherwise provided to, electronic system180. As will be apparent from the lists of examples previously given,electronic system 180 will often contain certain mechanical components(not shown) in addition to the circuit modules 170 and user interface182. It will be appreciated that the one or more circuit modules 170 inelectronic system 180 can be replaced by a single integrated circuit.Furthermore, electronic system 180 may be a sub-component of a largerelectronic system.

FIG. 19 shows a further embodiment of an electronic system as a computersystem 190. Computer system 190 contains a processor 192 and a memorysystem 194 housed in a computer unit 196. Computer system 190 is but oneexample of an electronic system containing another electronic system,i.e. memory system 194, as a sub-component. The computer system 190 maycontain an input/output (I/O) circuit 198 that is coupled to theprocessor 192 and the memory system 194. Computer system 190 optionallycontains user interface components that are coupled to the I/O circuit198. The I/O circuit 198 may be coupled a monitor 200, a printer 202, abulk storage device 204, a keyboard 206, and a pointing device 208. Itwill be appreciated that other components are often associated withcomputer system 190 such as modems, device driver cards, additionalstorage devices, etc. It will further be appreciated that the processor192 and/or the memory system 194 may include ultra-thin body SOI devicesaccording to an embodiment. Further, at least two of processor 192,memory system 194, and I/O circuit 198 of computer system 190 can beincorporated on a single integrated circuit. Such single packageprocessing units reduce the communication time between the processor 192and the memory system 194.

It will be readily understood to those skilled in the art that variousother changes in the details, material, and arrangements of the partsand method stages which have been described and illustrated in order toexplain the nature of this invention may be made without departing fromthe principles and scope of the invention as expressed in the subjoinedclaims.

1. A process of forming a semiconductor device comprising: providing agate stack upon a silicon-on-insulator (SOI) substrate; at the gatestack, forming a gate stack undercut; and at the undercut, growing anembedded epitaxial source/drain junction.
 2. The process according toclaim 1, forming a gate stack undercut further including: forming afirst spacer and a second spacer on the gate stack; growing an elevatedepitaxial first layer upon the substrate; removing the second spacer onthe gate stack; and at the gate stack, forming the gate stack undercut.3. The process according to claim 1, forming a gate stack undercutfurther including: forming a first spacer and a second spacer on thegate stack; growing an elevated epitaxial first layer upon thesubstrate; removing the second spacer on the gate stack to expose aportion of silicon on the SOI substrate; and etching the silicon on theSOI substrate under conditions that undercut the gate stack.
 4. Theprocess according to claim 1, forming a gate stack undercut furtherincluding: forming a first spacer and a second spacer on the gate stack;growing an elevated epitaxial first layer upon the substrate; removingthe second spacer on the gate stack to expose a portion of silicon onthe SOI substrate; and etching the silicon on the SOI substrate underconditions that undercut the gate stack at a rate from about 1 Å/secondto about 30 Å/second.
 5. The process according to claim 1, forming agate stack undercut further including: forming a first spacer and asecond spacer on the gate stack; growing an elevated epitaxial firstlayer upon the substrate; removing the second spacer on the gate stackto expose a portion of the silicon on the SOI substrate; and etching thesilicon on the SOI substrate with a sulfur hexafluoride (SF6) etchrecipe.
 6. The process according to claim 1, forming a gate stackundercut further including: forming a first spacer and a second spaceron the gate stack; growing an elevated epitaxial first layer upon thesubstrate; removing the second spacer on the gate stack; and etching theelevated epitaxial first layer and a portion of the silicon on the SOIsubstrate to form a gate-masked silicon residue and a lateral siliconresidue.
 7. The process according to claim 1, growing an embeddedepitaxial source/drain junction from the undercut further including:forming a first spacer and a second spacer on the gate stack; growing anelevated epitaxial first layer upon the substrate; substantiallyremoving the elevated epitaxial first layer under conditions to form theundercut, to expose a self-aligned region of the insulator of the SOIsubstrate, and a lateral residue of the silicon on the SOI substrate;and growing the embedded epitaxial source/drain junction underconditions that cause epitaxial silicon to form a closure seam betweenthe undercut and the lateral residue.
 8. The process according to claim1, further including: following growing an embedded epitaxialsource/drain junction, forming a salicided, raised epitaxial tip.
 9. Theprocess according to claim 1, further including: following growing anembedded epitaxial source/drain junction, forming a salicided,polysilicon epitaxial gate layer.
 10. A process of forming transistorcomprising: providing a gate stack upon a silicon-on-insulator (SOI)substrate; forming a first spacer and a second spacer on the gate stack;growing an epitaxial first layer upon the substrate; removing the secondspacer on the gate stack; at the gate stack, removing the epitaxialfirst layer while forming a gate stack undercut; and at the gate stackundercut, growing a source/drain epitaxial second layer.
 11. The processaccording to claim 10, forming a first spacer and a second spacer on thegate stack further including: depositing an oxide first layer over thegate stack; and spacer etching the oxide first layer.
 12. The processaccording to claim 10, forming a first spacer and a second spacer on thegate stack further including: depositing an oxide first layer over thegate stack; depositing a nitride second layer over the gate stack; andspacer etching the nitride second layer and the oxide first layer. 13.The process according to claim 10, forming a first spacer and a secondspacer on the gate stack further including: depositing an oxide firstlayer over the gate stack; spacer etching the oxide first layer to forman oxide first spacer; growing a nitride second layer over the gatestack and the oxide first spacer; and spacer etching the nitride secondlayer to form a nitride second spacer.
 14. The process according toclaim 10, wherein growing an epitaxial first film upon the substratefurther includes: forming a substantially undoped silicon epitaxiallayer upon the SOI substrate.
 15. The process according to claim 10,wherein forming a gate stack undercut includes: etching silicon of theSOI substrate that is exposed after removing the second spacer on thegate stack.
 16. The process according to claim 10, wherein forming agate stack undercut includes: etching silicon of the SOI substrate thatis exposed after removing the second spacer on the gate stack; andetching at least a portion of the epitaxial first film.
 17. The processaccording to claim 10, wherein growing a source/drain epitaxial secondlayer at the gate stack undercut includes: chemical vapor depositiongrowing the source/drain epitaxial second layer under conditions thatcause the epitaxial second layer to grow from the gate stack undercuttoward gate stack-lateral SOI silicon residue.
 18. The process accordingto claim 10, further including: over the SOI substrate, forming arefractory metal layer.
 19. The process according to claim 10, furtherincluding: over the SOI substrate, forming a refractory metal layer;treating the source/drain epitaxial second layer and the refractorymetal layer to form a salicided raised epitaxial tip.
 20. The processaccording to claim 10, further including: upon the gate stack, growing apolysilicon epitaxial second layer; upon the polysilicon epitaxialsecond layer, forming a refractory metal layer; and treating thepolysilicon epitaxial second layer and the refractory metal layer toform a salicided gate layer.
 21. An embedded source/drainsilicon-on-oxide (SOI) junction, comprising: a gate stack disposed uponan SOI substrate, the gate stack including an undercut; and an epitaxiallayer disposed in the undercut.
 22. The embedded source/drainsilicon-on-oxide (SOI) junction according to claim 21, wherein theepitaxial layer has a thickness in a range from about 100 Å to about1,500 Å, and wherein the epitaxial layer is selected from an n-dopedlayer and a p-doped layer.
 23. The embedded source/drainsilicon-on-oxide (SOI) junction according to claim 21, wherein theepitaxial layer has a thickness in a range from about 100 Å to about1,500 Å and further including: a salicided raised epitaxial tip disposedin the epitaxial layer and adjacent to the gate stack.
 24. The embeddedsource/drain silicon-on-oxide (SOI) junction according to claim 21,wherein the epitaxial layer has a thickness in a range from about 100 Åto about 1,500 Å, wherein the epitaxial layer is selected from ann-doped layer and a p-doped layer, and further including: a salicidedpolysilicon gate layer disposed above and on the gate stack.
 25. Theembedded source/drain silicon-on-oxide (SOI) junction according to claim21, wherein the epitaxial layer has a thickness in a range from about100 Å to about 1,500 Å, wherein the epitaxial layer is selected from ann-doped layer and a p-doped layer, and further including: a salicidedraised epitaxial tip disposed in the epitaxial layer and adjacent to thegate stack; and a salicided polysilicon gate layer disposed above and onthe gate stack.
 26. The embedded source/drain silicon-on-oxide (SOI)junction according to claim 21, further including: a SOI channelembedded beneath the gate stack, wherein the gate stack includes apolysilicon gate electrode with a width, W, and wherein the SOI channelincludes a channel length less than width, W.
 27. The embeddedsource/drain silicon-on-oxide (SOI) junction according to claim 21,further including: a SOI channel embedded beneath the gate stack,wherein the gate stack includes a polysilicon gate electrode with awidth, W, and wherein the SOI channel includes a channel length in arange from about 0.2 W to about 0.99 W.
 28. A system, comprising: acircuit module, wherein the circuit module includes at least one siliconon insulator (SOI) substrate, wherein the SOI substrate includes: a gatestack disposed upon an SOI substrate, the gate stack including anundercut; and an epitaxial layer disposed in the undercut a substrate.29. The system according to claim 28, wherein the circuit module isdisposed in a host selected from a clock, a television, a cell phone, apersonal computer, an automobile, an industrial control system, and anaircraft.
 30. The system according to claim 28, further including: aprocessor; an input/output (I/O) circuit coupled to the processor.